Improving nutrition efficiency and milk quality in dairy production

Milk is the most nutritious single food but also a major provider of saturated fatty acids (SFA) in the UK diets. Certain SFA may increase risk of cardiovascular disease (CVD), and health organisations have urgently recommended substitution of dietary SFA with cis-unsaturated FA (UFA), to reduce CVD-related illness. Producing milk, the main single source of fatty acids (FA) in human diets, with more UFA and less SFA could
contribute to this aim without requiring changes to consumer dietary habits. Additionally, the increasing global demand for milk and dairy products, and the competition for resources for food, feed and fuel require optimum use of resources in all aspects of dairy production. Improving feed use efficiency (FUE; more milk per given feed intake) and energy use efficiency (EUE; higher % of ingested energy retained in
the body) increase farm profitability (lower feeding costs) and reduce environmental footprint (lower methane emissions) of milk production. Therefore, developing win-win management scenarios that simultaneously improve efficiency and milk nutritional quality are of paramount importance for future sustainability, and improving consumer perception, of the dairy sector. The aim of the proposed programme is therefore to identify the animal, dietary, and management factors that improve FUE and EUE in dairy cows and enhance the nutritional quality of milk. This will be achieved via the following studies:1) Investigate the effects of, and interactions between, the main dietary parameters on FUE, NUE and methane emissions. A dataset of >100 cow metabolism studies, will be developed from existing data (URE, AFBI), and enhanced with published data, using studies that preferably contain variables related to diet, animal, feed intake, production, energy intake/outputs, and methane emissions. Analysis of variance (ANOVA) using linear mixed effects models (LME) will assess the effect of nutrient parameters on FUE, EUE and methane emissions. Multivariate redundancy analyses (RDA) will assess the relative impact and graphically represent relationships between dietary parameters, and the responses they evoke on FUE, EUE, methane emissions and milk quality. 2) Investigate the relative impact of husbandry practices (breeding, feeding, management) on FUE and milk nutritional quality at herd level. A farm survey including 25 organic and 45 conventional farms was conducted January-December 2019 (URE). This study collected monthly milk samples from farms' bulk-tank and recorded husbandry practices and production variables (milk yield, basic composition, FUE) via farmers' questionnaires. During the proposed programme, milk samples will be analysed for FA profiles by gas chromatography. ANOVA LME will assess the effect of production system (organic, conventional) and within-system husbandry-groups (e.g. high-grazing vs lowgrazing) on FUE and milk quality. RDA will be performed to assess the relative impact and graphically represent the relationships between husbandry parameters, and the responses they evoke on FUE, productivity and milk quality. 3) Reveal how rumen microbes influence metabolic pathways related to FUE, EUE, methane emissions and milk quality under different dairy diets. An experiment with 12 lactating dairy cows will be performed in AFBI, using three different diets containing white clover under a 3(diets)x3(periods) Latin-Square design. In each period, cows will be housed in cubicle accommodation for 21 days and then in indirect open-circuit respiration calorimeter chambers for the final 7 days, to measure feed intakes, milk production, urine/faeces output, gaseous exchange (O2, CO2 and CH4) and collect rumen fluid and milk samples. Milk/rumen FA profiling (URE) and metagenomics techniques (QUB) will be used to identify rumen microbes, and their genes, which promote FUE, EUE and milk quality. The metabolite profile in rumen fluid and milk, by 500MHz NMR (URE), will highlight the metabolic pathways related